1. Field of the Invention
The present invention relates to a hairless mouse designated NS:Hr/ICR which is sensitive to Helicobacter pylori. The alimentary canal of the NS:Hr/ICR hairless mouse is infected orally by H. pylori. The NS:Hr/ICR hairless mouse is used as an experimental model for H. pylori infection.
2. Description of the Related Art
It has been believed for a long time that within the alimentary canal of animals including humans, microorganisms can exist only in the intestine where the pH environment is nearly neutral, and that most microorganisms cannot live in the stomach where the pH environment is acidic and the pH value is 2 or lower. However, the study of the cause and pathology of gastric and duodenal diseases has greatly been changed since J. R. Warren and B. Marshall made it clear in 1983 that H. pylori, which is a microaerophilic and spiral Gram negative bacillus, affects gastritis, gastric ulcer and duodenal ulcer (The Lancet, 1273, 1983).
More than ten years have passed since the discovery of H. pylori and it is now confirmed that the infection by H. pylori in gastric mucosa causes the chronic inflammation of the gastric mucosa, inducing peptic ulcer and leading to gastroduodenal ulcer, and that this chronic inflammation when prolonged leads to atrophic gastritis, further leading to the formation of tumor through the formation of neoplasm on the mucosal epithelium. Moreover, in June, 1994, WHO counseled on the basis of the epidemiological investigation that H. pylori is a first class carcinogen.
Under these circumstances, an appropriate animal model is essential for demonstrating that H. pylori affects the chronic inflammation of the gastric mucosa, gastroduodenal ulcer and the formation of tumor. With the establishment of an experimental animal model, it would be possible to elucidate the mechanism of the development of diseases by H. pylori, such as gastritis, gastric ulcer and duodenal ulcer as well as the formation of tumor through the formation of neoplasm on the mucosal epithelium. Accordingly, many experiments on H. pylori infection have been carried out by using animals such as rats, mice, rabbits, dogs, pigs or monkeys. It has been reported that the infection and fixation of H. pylori into big animals such as sterilized porcine, sterilized beagle, and monkey were successful but that the infection into small animals such as mice and rats was not easy. Although many experiments on the H. pylori infection have been made under various conditions wherein sterilized animals and antibiotics are used, gastric acid is neutralized and the secretion of gastric juice is controlled, no satisfactory result has been obtained.
Recently, it was reported that both nude and euthymic mice were successfully infected with H. pylori and that the infection of euthymic mice was only temporary (Karita M. et al, New Small Animal Model for Human Gastric Helicobacter pylori Infection: Success in Both Nude and Euthymic Mice, Am. J. of Gastroenterology, Vol. 86, 1596, 1991). It was also reported that Mongolian gerbils were infected successfully by H. pylori (Yokota K. et al, Colonization of Helicobacter pylori in the Gastric Mucosa of Mongolian Gerbils, Microbiol. Immunol. Vol. 35(6), 475, 1991). The present inventors carried out the same experiment but could not confirm the continued infection of H. pylori. Further, Marta Marchetti et al have reported in Science, Vol. 267, Mar. 17, 1995, pages 1655-1658 about the ability of fresh clinical isolates and strains of H. pylori to infect specific pathogen-free (SPF)CDI mice, conventional BALB/c and CDI mice.
Under these circumstances, a new small animal model for H. pylori infection has been required, which is sensitive to H. pylori, easy to breed, easy to orally infect and easy to handle.